The Importance of Cylinder Drop Testing and Inductive Ignition Testing in Marine Engine Surveys

These graphs were taken from my diagnostics computer when I was conducting a cylinder drop test on a Mercury Verado, in-line six cylinder, 2.6 liter, supercharged 250 HP outboard engine.

2.6L 250 VERADO Cylinder Drop Test Chart - 12Aug16 - Ehri

Normal cylinder drop graph while the engine is running

The graph to the right with the significant drop is of a normal engine when I used my diagnostics computer to shut down the ignition on one cylinder while the engine was running. This test is conducted to test each cylinder’s power compared to the rest of the cylinders. This test typically works best with a slight load on the engine to bring out the difference in power when dropping each cylinder.

The diagnostics computer connects to the engine’s EMM (engine’s computer) and through my diagnostics computer I give commands to the EMM to drop each cylinder one by one. As this is done, when a faulty or dead cylinder is detected no change (or very little change) will be detected like on the graph (seen below). I will typically use an inductive clamp DVOM to verify the bad cylinder and to see the secondary voltage being produced by the ignition coil.

Stbd Engine CYl 4 - 07 5.7 MIE FWC DTS Cylinder Drop Test Chart - 06May16 19h28m46s

Abnormal cylinder drop (discovery of a non-working cylinder)

In sea trials, the dead cylinder can hide and the engines can still reach their rated wide open throttle range. This is why having a marine surveyor that conducts this testing is so important. Missing a dead cylinder can cost a potential buyer hundreds if not thousands of dollars after he / she has purchased the vessel and the surveyor (who does not do this testing or have any factory engine training) has stated in the report that the engines were in good working order and that they achieved their rated WOT range.


Inductive ignition testing of the ignition coils on an outboard engine

I took a video of a cylinder drop test on a pair of Mercury Optimax engines that had a dead ignition coil on the starboard engine. The video is at the link below:

Come see more about my marine engine survey services at:

Capt. John Banister, AMS®
Suenos Azules Marine Surveying and Consulting
4521 PGA Boulevard, Suite 461
Palm Beach Gardens, Florida 33418
SAMS® Accredited Marine Surveyor
ABYC® Standards Accredited
Yamaha Certified Outboard Marine Technician
Mercury / MerCruiser Certified Technician
Honda Certified Outboard Engine Technician
USPAP® Certificate on Appraisal Standards
ITC® Certified Level II Thermographer
USCG Licensed Master Captain
Member SAMS®, ABYC®, IAMI®, & NFPA®

About suenosazules

I own and operate a marine surveying and consulting firm based in Palm Beach Gardens, Florida. We offer pre-purchase, insurance, valuation, damage claim, marine engine diagnostics, and ultrasonic marine surveys. I also provide service and repair services for gasoline outboard and inboard engines. I am a USCG licensed master captain and provide charter and yacht deliveries for both power and sailing vessels. We provide our services in the United States, the Caribbean Islands, Puerto Rico, Belize, and Costa Rica. We specialize in surveying and inspecting boats for overseas buyers in Europe, Asia, Australia, and Africa. I am a SAMS® Accredited Marine Surveyor, ABYC® Standards Accredited, a Yamaha Certified Outboard Engine Technician, a Mercury / MerCruiser Certified Technician, a Honda Certified Outboard Engine Technician, a ITC® Certified Level II Thermographer, holds a USPAP® Certificate on Appraisal Standards, a USCG Licensed Master Captain, and a member of SAMS®, ABYC®, IAMI®, and the NFPA®.
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